This disclosure generally relates to motion control and specifically to generation of constraint-based, preferably time-optimal motion profiles. The invention relates to a device for moving an object and to a method for moving an object.
Most automation applications require a motion control system to control e.g. a position of a moving object. Such motion control systems typically comprise a device for moving an object including a control unit, one or more motors or similar actuating devices operating under the guidance of said device, which sends position control instructions to the motor. In a common architecture, the device sends the control instructions to a motor drive and the motor drive controls the driving current output to the motor in accordance with the control instructions, facilitating the controlled movement of the motor.
If the device determines that the object must move to a new position, set points must be calculated, which are used as an input value for said control unit and which represent a desired position or velocity at a specific time for the object in motion. For the calculation of said set points a set point generator means is used. To this end an algorithm deployed within said device is typically used. Said algorithm determines a set point profile, which represents set points as a function of time. Said algorithm also determines the first up till nth derivative of this function of time. If the function of time represents e.g. a position, said derivatives represent e.g. velocity, acceleration, jerk and possibly higher derivatives like the snap and the crackle as a function of time.
Once the set point profile is calculated, the control unit translates the set point profile into appropriate control signaling for moving the object along a trajectory, i.e. a path for the object along a single line or within a working cell. Many industrial applications require time-optimal solutions with low vibrations and a minimized lag during a change in system stage, e.g. high precision machines employed in the semiconductor industry.
Typical set point generators use algorithms that produce second or third order polynomial profiles or S-curve profiles. While the aforementioned second or third order polynomial profiles are normally not smooth enough for low vibrations, the aforementioned S-curve profiles are normally not time-optimal. Thus these known standard motion system have a limited control performance. Pure numerical higher order solutions with time-optimal profiles are complex and demand a very high computing power.
For the foregoing reasons there is a need for a solution for increased control performance, especially in high precision environments considering limitations in computing power.